The invention relates to hinge joints in general, and more particularly to improvements in hinge joints which can be used to pivotally secure the back rest to the body supporting portion of a seat, e.g., the driver's seat or a passenger seat in a motor vehicle. Still more particularly, the invention relates to improvements in hinge joints of the type wherein a first component is affixed to the body supporting portion of the seat, a second component is affixed to the back rest of the seat, and the second component can turn relative to the first component about the axis of a pintle or shaft which pivotally connects the second component to the first component.
Hinge joints of the above outlined character are normally provided with a set of gears or a like device which serves to pivot the second component relative to the first component between a plurality of different positions and includes means for releasably holding or locking the second component in a selected angular position relative to the first component. As a rule, the pintle carries an eccentric which mounts one of the components, for example, the first component.
Commonly owned German Pat. No. 30 13 304 to Wilking et al. discloses a hinge joint wherein the eccentric comprises a motion transmitting member which is non-rotatably connected with the pintle and two arcuate sections which surround a portion of the pintle and flank the motion transmitting member. Each arcuate section has a first end which is adjacent the motion transmitting member and a second end, and the eccentric further comprises a spring which biases the second ends of the sections away from each other. The arrangement is such that the convex peripheral surfaces of the arcuate sections are biased against a surface surrounding an opening in the one component during each stage of utilization of the patented hinge joint, i.e., when the back rest is held in a selected angular position as well as while the back rest is in the process of changing its angular position relative to the body supporting portion of the seat. The extent of frictional engagement between the peripheral surfaces of the sections and the one component is temporarily reduced during the initial stage of each angular adjustment of the back rest relative to the body supporting portion of the seat. However, the force which is being applied to the back rest in order to change its angular position promotes frictional engagement between the peripheral surfaces of the sections and the internal surface of the one component of the hinge joint. Therefore, it was already proposed to reduce friction between the sections and the one component by reducing the area of the peripheral surfaces of the sections. This, in turn, entails pronounced wear upon the peripheral surfaces and the development of large specific pressure between the sections and the one component of the hinge joint. Therefore, a person wishing to change the angular position of the back rest must exert a substantial force which is particularly undesirable when the angular position of the back rest is to be changed by a person who already occupies the body supporting portion of the seat, by an adolescent, by an elderly person or by a person who is weakened as a result of illness and/or for other reasons. Moreover, the wear upon the parts of the eccentric and upon the one component of the hinge joint is very pronounced.